Free Forms and Functions of Plants MCQs with Answers

181. Size of the flower of chrysanthemum may be enlarged by removing

• A. All leaves
• B. A few leaves
• C. All branches except one
• D. All floral bud except one

Explanation: Removing all floral buds except one is the correct method to promote the growth of larger chrysanthemum flowers. By focusing the plant's energy on a single bud, it can develop into a larger flower. The other options either hinder the plant's growth or do not effectively promote larger flower size.

182. The critical day length of Hyoscyamus for flowering is :

• A. 15.5 hours
• B. 9 hours
• C. 11 hours
• D. 13 hours

Explanation: Hyoscyamus, like many plants, has a specific photoperiod requirement known as the critical day length, which is the minimum daylight hours necessary to trigger flowering. For Hyoscyamus, this is 15.5 hours. If the day length is less, the plant will not flower. The other options provide shorter day lengths, which are insufficient to meet the plant's photoperiodic needs. Understanding photoperiodism is crucial in botany, as it significantly influences plant development and reproductive cycles.

183. Growth movement of pollen tube towards the egg is:

• A. Hydrotropism
• B. Chemotropism
• C. Chemotactic
• D. Seismetactic

Explanation: Chemotropism: Chemotropism is the growth movement of a plant part towards or away from a chemical stimulus. In the context of a pollen tube, it can refer to the growth movement towards the chemical signals released by the egg.Therefore, the most appropriate option for the growth movement of a pollen tube towards the egg is 'Chemotropism,' as it involves the growth response towards the chemical signals released by the egg.

184. Opening of flower buds and leaf buds is called;

• A. Epinasty
• B. Thermonasty
• C. Photonasty
• D. Seismonasty

Explanation: Epinasty refers to the downward or outward bending or opening of flower buds or leaf buds. It is a type of tropism, specifically a growth response in which the upper side of the bud or leaf grows slower than the lower side, resulting in the bending or opening of the bud or leaf.

185. The hormone that causes seed and bud dormancy in plants is called

• A. Auxins
• B. Ethylene
• C. Abscisic acid
• D. Gibberellins

Explanation: Abscisic acid is a plant hormone that plays a crucial role in inducing and maintaining seed and bud dormancy. It is responsible for inhibiting growth and promoting dormancy in plants, especially in adverse environmental conditions.

186. The changes in the biochemical composition and physiology occurring at regular intervals in 24 hours is termed as:

• A. geoannual rhythm
• B. lunar rhythm
• C. circadian rhythm
• D. tidal rhythm

Explanation: Circadian rhythms are intrinsic 24-hour cycles that affect physiological, mental, and behavioral functions in living organisms. These rhythms align with the Earth's rotation, resulting in predictable changes in response to light and dark cycles. The incorrect options are:Geoannual rhythm: Relates to yearly changes, not daily.Lunar rhythm: This rhythm is based on the moon's phases, approximately 29 days long.Tidal rhythm: These rhythms are dictated by tidal patterns, typically occurring over about 12 hours, not 24 hours.

187. All the following are growth hormones, except

• A. phytohormones
• B. Gibberllin
• C. auxins
• D. cytokinesis

Explanation: All plant hormones are collectively known as growth hormones. They include growth promoters, e.g., auxins, cytokinins, gibberellins, etc. as well as growth inhibitors such as abscisic acid, etc. All of the options except option 'A' are growth hormones; thus, option 'A' is the correct answer. This division is further explained by the following diagram:

188. Abscisic acid promotes:

• A. Triple response
• B. Sex expression
• C. Flower initiation
• D. Leaf, flower, and fruit fall

Explanation: Abscisic acid (ABA) is a plant hormone that plays a key role in inhibiting growth and promoting dormancy in plants. It is particularly known for its role in the abscission or shedding of leaves, flowers, and fruits, especially under stress conditions such as drought. This is why it is sometimes referred to as the 'stress hormone.' The other options relate to functions typically influenced by other hormones: the triple response is associated with ethylene, sex expression is influenced by gibberellins and ethylene, and flower initiation is promoted by gibberellins.

189. Growth promoting substance in plant is:

• A. F.A.D
• B. Chlorophyll a
• C. I.A.A
• D. ABA

Explanation: The correct answer is I.A.A (Indole-3-acetic acid), which is an auxin, a class of plant hormones that are essential for cell elongation, root development, and various other growth processes. Auxins like I.A.A are key in regulating plant growth and encouraging developmental changes.F.A.D is unrelated to growth promotion because it functions primarily in energy transfer and redox reactions. Chlorophyll a is essential for photosynthesis, converting light energy into chemical energy, but it is not a hormone involved in growth promotion. ABA, while important for stress response and dormancy, acts more as a growth inhibitor rather than a promoter.

190. Tobacco is a:

• A. Long day plant
• B. Short day plant
• C. Day-neutral plant
• D. Intermediate plant

Explanation: Tobacco is classified as a short-day plant. These plants require long periods of darkness and shorter daylight hours to initiate flowering. This characteristic is typical in plants that flower in early spring or autumn. On the contrary, long-day plants require longer daylight hours to flower, day-neutral plants do not depend on photoperiods for flowering, and intermediate plants have varying requirements not strictly tied to day length.